Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$50.81	11.166%	$56.4834	$56.48	$56.50	$56.50
Purchase #2	$148.55	9.133%	$162.1171	$162.12	$162.10	$162.10
Purchase #3	$28.90	13.529%	$32.8099	$32.81	$32.80	$32.80
Purchase #4	$164.47	5.116%	$172.8843	$172.88	$172.90	$172.90
Purchase #5	$73.58	10.124%	$81.0292	$81.03	$81.05	$81.00
Purchase #6	$31.83	5.793%	$33.6739	$33.67	$33.65	$33.70
Purchase #7	$192.85	6.541%	$205.4643	$205.46	$205.45	$205.50
7 purchase totals =	$690.99		$744.4621	$744.45	$744.45	$744.50